1. Field of the Invention
The present invention relates to an ocular light stimulus apparatus, and more particularly relates to an ocular light stimulus apparatus for providing localized light stimulus to a retina of an ocular fundus under examination by stimulus light from a stimulus light source to perform biological examination through use of a bioelectrical signal from the retina.
2. Description of the Prior Art
Conventional known methods used primarily for ophthalmic examination include not only capturing a fundus image and performing fundus examination, but also electroretinogram (ERG) examination in which stimulus light is radiated to a retina, an action potential generated in the retina is measured, and an electroretinogram is created to perform an ophthalmic biological examination.
In an ERG examination, a background light is needed for illuminating the background onto which the stimulus light is radiated, and the quality of the ERG examination is determined by the proper combination of background light intensity and stimulus light intensity. Japanese Journal of Ophthalmology, Vol. 92, No. 9 (Sep. 10, 1988, 5-(1423) to 11-(1429)) describes the effects obtained from an ERG examination (local ERG) when stimulus light is radiated in localized fashion to a point on the macula of the fundus using visible background light.
Japanese Examined Patent Application Publication No. 1987-16090 discloses a light stimulus apparatus in which stimulus light is radiated to an ocular fundus under examination using a fundus camera, and electrical information obtained through the light stimulus is displayed as an electroretinogram. Japanese Examined Patent Application Publication No. 1987-20809 proposes a technique for observing which portions are stimulated in what manner by local ERG stimulus light while observing a wide range of the fundus by infrared light.
Furthermore, Japanese Examined Patent Application Publication No. 1992-19852 discloses that an ocular fundus under examination is observed without dilation, and a beam of light for observing and imaging the eye under examination is used as stimulus light. Japanese Laid-open Patent Application No. 2005-323815 discloses that a light stimulus apparatus for radiating stimulus light to a fundus is attached as a unit to a fundus camera to perform ERG examination. Japanese Laid-open Patent Application No. 2006-42952 discloses that, to perform local ERG examination, the entire retinal area is irradiated by white light using a white-light-emitting diode with this illumination used as a background, and a stimulus light spot is radiated from a high-luminance light-emitting diode while observing the fundus by infrared light.
In an ophthalmic examination apparatus, a light source (fixation lamp) used for ophthalmic examination is moved on a plane perpendicular to the optical axis (Japanese Laid-open Patent Application No. 1987-144635 and Japanese Patent No. 2736780).
In the conventional techniques, the position of the stimulus light source or the size of the stimulus light is not varied when the local ERG examination is performed, and as a result, drawbacks occur in that a bioelectric signal is not obtained from an arbitrary position of the retina, and a reliable local ERG examination is difficult to perform.
When the stimulus light projection position is varied in the local ERG examination, drawbacks also occur in that the projection position is not easily maintained at a prescribed position, and a reliable bioelectric signal is difficult to obtain from the retina.
It is therefore an object of the invention is to provide an ocular light stimulus apparatus capable of performing a reliable local ERG examination with a simple structure.